title: Muscarinic receptor subtypes and receptor-coupled phosphatidylinositol hydrolysis in rat bladder smooth muscle.
abstract: BACKGROUND
  The purpose of this study was to evaluate the muscarinic receptor subtypes expressed in rat bladder smooth muscle and characterize the muscarinic receptor-coupled phosphatidylinositol (PI) hydrolysis in order to clarify the first step of bladder smooth muscle contraction.
  
  
  METHODS
  Expressions of mRNAs of muscarinic receptor subtypes were examined by Northern blot analysis. Changes in the mass of inositol 1,4,5-trisphosphate (IP3) and the inhibitory effects of muscarinic subtype specific antagonists on PI hydrolysis were determined after carbachol stimulation.
  
  
  RESULTS
  mRNAs of m2 and m3 genes, encoding M2 and M3 receptors, were expressed in rat bladder smooth muscle. Carbachol produced a rapid increase of IP3, which returned to the basal level within 30 seconds. 4-Diphenylacetoxyl-N-methylpiperidine methiodide (4-DAMP; M1 and M3 antagonist) strongly inhibited the PI hydrolysis, but methoctramine (M2 antagonist) partially inhibited it at 10(-4) mol/L. The IC50 value for atropine was 9.5 x 10(-9) mol/L, for pirenzepine 6.4 x 10(-6) mol/L, and for 4-DAMP 1.5 x 10(-7) mol/L.
  
  
  CONCLUSIONS
  M2 and M3 receptors are expressed in rat urinary bladder. Only M3 receptor was involved in the production of IP3, which might induce the initial phase of contractile response in rat bladder smooth muscle after carbachol stimulation.
authors.affiliation: Department of Urology, Oita Medical University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Mimata
authors.forename: Y
authors.initials: Y
authors.lastname: Nomura
authors.forename: A
authors.initials: A
authors.lastname: Emoto
authors.forename: J
authors.initials: J
authors.lastname: Latifpour
authors.forename: M
authors.initials: M
authors.lastname: Wheeler
authors.forename: R M
authors.initials: RM
authors.lastname: Weiss
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D017931:DNA Primers / Q000737:chemistry; D015870:Gene Expression; D006868:Hydrolysis; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000235:genetics / Q000378:metabolism*; D001743:Urinary Bladder / Q000166:cytology / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D010716:Phosphatidylinositols; D012333:RNA, Messenger; D011976:Receptors, Muscarinic; D015544:Inositol 1,4,5-Trisphosphate